Reduced friction watch cannon shafts

ABSTRACT

An otherwise conventional watch is provided with an additional bearing element to reduce friction between two coaxial tubes that carry the minute hand and the hour hand respectively. The bearing may be located between the two tubes or outside the outer tube.

United States Patent [19;

Hetzel et al.

[ REDUCED FRICTION WATCH CANNON SHAFTS Inventors: Max Hetzel, Bienne; Hans Kocher,

Buren, both of Switzerland [73] Societe Suisse pour llndustrie Horlogere Management Services S.A., Bienne, Switzerland Filed: Apr. 8, 1974 Appl. No.: 458,813

Assignee:

[30] Foreign Application Priority Data Apr. 18. 1973 Switzerland 005839/73 U.S. Cl. 58/138 Int. Cl. .1 G04b 13/02 May 27, 1975 [58] Field of Search 58/140 R, 138

[56] References Cited UNITED STATES PATENTS 95l,139 3/l9l0 Mehl 58/133 Primary Examiner-George H. Miller, Jr. Attorney, Agent, or Firm-Griffin, Branigan and Butler [5 7] ABSTRACT An otherwise conventional watch is provided with an additional bearing element to reduce friction between two coaxial tubes that carry the minute hand and the hour hand respectively. The hearing may be located between the two tubes or outside the outer tube.

6 Claims, 4 Drawing Figures PATENTEDMAT 27 ms FIG. 1 (PRIOR ART) REDUCED FRICTION WATCH CANNON SHAFTS BACKGROUND OF THE INVENTION The present invention relates to watches having at least approximately coaxial minute and hour tubes which rotate with different speeds in the same direction, and from which extend the minute hand and the hour hand, respectively. Almost all known watches employing an analog time display include such an arrangement. In addition to the two coaxial tubes :1 watch is frequently provided with a coaxial axle which carries a second hand and rotates inside the tube to which the minute hand is fixed.

It is well known that watches, particularly wrist watches with electrical or electronic driving devices, such as a balance. a tuning fork or a crystal, have very little power left at the hour wheel to drive a calendar mechanism. This is understandable if one considers that watches of this kind are powered by batteries of 80 to I mA/h which must drive the watch for at least a whole year. Usually a power of about lptW is available at the hour wheel to drive a calendar device or any other mechanism. In the past, great effort has been made to reduce the friction and power losses of the gear train so as to have a higher efficiency between the driving device and the display. This would, particularly in electrically or electronically powered watches, make available at the hour wheel the power necessary to drive a calendar device. Until now such efforts to increase the efficiency have been directed toward producing higher quality toothings and bearings. However, due to the fact that these elements already provide a very good power transmission, no substantial power gain could be obtained at the hour wheel without increasing the initial power of the driving device. Insofar as applicant is aware, no one has ever calculated how much power is lost, or calculated how efficient the conventional arrangement and bearing of the two tubes carrying the minute and the hour hand respectively is, and considered whether or not the power transmission of that part of the gear train could possibly be improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a watch in which the bearings of the minute and the hour tubes respectively permit a higher efficiency and better power transmission than the arrangements now known.

In accordance with the principles of the present invention, a watch having two substantially coaxial tubes carrying the minute and hour hands, respectively, is provided with an additional bearing element located between the two coaxial tubes and affixed to the base plate of the watch. In an alternative embodiment, the bearing element may be disposed so as to surround the outermost of the two tubes.

Other objects of the invention and its mode of operation will become apparent upon consideration of the following description and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. I is a top sectional view of a conventional watch;

FIG. 2 is a top sectional view of a watch according to the invention;

FIG. 3 is a top sectional view of a different embodiment of the invention wherein the bearing element surrounds both coaxial tubes; and,

FIG. 4 is a partial front sectional view of a watch ac cording to FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. I shows a conventional prior art watch having a second hand in the center, an hour wheel I driven by a pinion 2 and carrying an hour tube 3 onto which an hour hand (not shown) may be affixed. A pinion 4 be longs to a calendar mechanism (not shown). Inside the hour tube 3 rotates a minute tube 5 onto which may be affixed a minute hand (not shown). Located inside the tube 5 is a fixed tube 6, in the center of which can rotate an axle carrying a second hand (both not shown). During the running of the watch the hour tube 3 rotates once every l2 hours, the minute tube 5 once every hour and a possible second hand axle (reference number 12 in FIG. 4) once every minute around their respective centers 3a, 5a and 12a.

In a watch including a calendar device the hour wheel 1 is subjected to two forces K one of which results from the driving pinion 2 and the other of which results from the pinion 4 of the calendar device. Between the hour tube 3 and the minute tube 5 a friction and braking effect takes place which results in an important power loss. This power loss is due to the fact that the minute tube 5 is squeezed between the hour tube 3 and the fixed tube 6 by the two forces 2K. Such a conventional bearing of the hour wheel I results in inefficient power transmission. This can easily be proved by means of the following calculation of the power loss and the efficiency of the power transmission arrangement.

Hereinafter the following symbols are used in simplified formulas:

N power used to drive a calendar device K force transmitted from the pinion 2 to the hour wheel 1 and from the latter to the pinion 4 of the calendar device Nv power loss Da outer diameter of the hour wheel 1 da outer diameter of the minute tube 5 di inner diameter of the minute tube 5 a coefficient of friction "r; efficiency It is known that K1r(Da) [12)(3600) and 1r(da) n-(di) Nv2Ka 3600 +2Ka 3600 Solving both equations for K, setting the solutions equal to each other, and solving for Nv, gives (da +di) Nv 24 0: N,

If the embodiment according to FIG. 1 has the followmg typical geometrical dimensions:

Assuming that the friction coefficient a is about 0.15 the efficiency i amounts to 1; 50 percent (3) Consider now the embodiment of FIG. 2 which differs from FIG. 1 only in that it includes a fixed bearing tube 7 between the hour tube 3 and the minute tube 5, so that both rotating tubes 3 and 5 bear against the immovable bearing tube.

The power loss of a watch presenting identical geometrical dimensions as the embodiment described above. but including a fixed tube according to the invention may be calculated as follows. It is known that 2 Ka1r(da) (Ill l3600l N and Solving both equations for K. setting the solutions equal to each other. and solving for N1- gives If da and Du are replaced by their assumed values.

Zllll at. lvl

With this kind of pow er transmission. the efficiency 17 amounts to "I; 95 percent i4) From a comparison of Equations I l J and (31 it is obvious that the bearing of the hour wheel I in accordance with the invention produces a much smaller power loss than does the conventional solution. Ac cordingly, the efficiency of the new embodiment is much higher than that of the known arrangements as is apparent from a comparison of Equations (2| and [4 Consequently a watch according to the invention provides at its hour wheel I a much higher power than does a watch of the convention type. even if the initial power of the driving device is equal in both watches.

FIG. 3 shows an alternate embodiment of the invention which differs slightly from that described above and shown in FIG. 2. The alternative embodiment comprises a fixed bearing tube 7 which is located outside the hour tube 3 and not between the latter and the min ute tube 5 as in the embodiment of FIG. 2. If the bearing tube 7 is precisely formed. the hour tube 3 can never touch the minute tube 5 which rotates around the other fixed tube 6. This embodiment presents the advantage that almost every conventional watch can easily be modified to incorporate the invention. In fact, it is enough to fit a tube 7 into the central opening of the bridge 11 of the calendar device (FIG. 4).

FIG. 4 shows in a partial schematic cross-sectional view how the embodiment according to FIG. 2 may be realized. the same reference numbers being used to identify like parts in the two views. The gear train 8 is of a conventional type. The wheel 9 is. in contrast to conventional watches. located under the plate 10. Only the pinion 2 lies above the plate 10 and under the bridge 11 of the calendar device. The fixed bearing tube 7 which separates the two rotating tubes 3 and 5 respectively, is affixed to the base plate 10. Located inside the minute tube 5 is a second hand axle 12. The bearing tube 7 according to the invention may be made of any conventional bearing material such as. for instance. ruby. beryllium, glucydur. steel. new silver or even brass.

The invention is particularly useful in watches driving a calendar device through the hour wheel. but can also serve in all other types of watches and clocks driving any other mechanism by means of the hour wheel.

It is obvious that various modifications and substitutions may be made in the described embodiments of the invention without departing from the spirit and scope of the invention as defined by the appended claims.

50 it is for instant possible to design the two embodiments described above and shown in FIG. 2 and FIG. 3 respectively without the fixed tube 6. as it becomes apparent from FIG. 4.

We claim:

1. In a watch having at least approximately coaxial minute and hour tubes respectively which rotate with different speeds in the same direction and from which one carries the minute hand and the other the hour hand. the improvement comprising a bearing element for preventing friction between said tubes.

2. The improvement as claimed in claim 1. in which the bearing element is it bearing tube affixed to the base plate of the watch and extending between said minute and hour tubes.

3. The improvement as claimed in claim 1, in which the bearing element is a tube affixed to a bridge of the watch and located outside the hour tube.

4. The improvement as claimed in claim 1. in which the hour tube is heared on the outside of the bearing 6 element and the minute tube on the inside of said hear- 6. The improvement as claimed in claim I, in which mg element the bearing element is made of ruby, beryllium, glucy- 5. The improvement as claimed in claim 1, in which the hour tube is part of an hour wheel which drives a calendar device. 5

dur steel, new silver, or brass. 

1. In a watch having at least approximately coaxial minute and hour tubes respectively which rotate with different speeds in tHe same direction and from which one carries the minute hand and the other the hour hand, the improvement comprising a bearing element for preventing friction between said tubes.
 2. The improvement as claimed in claim 1, in which the bearing element is a bearing tube affixed to the base plate of the watch and extending between said minute and hour tubes.
 3. The improvement as claimed in claim 1, in which the bearing element is a tube affixed to a bridge of the watch and located outside the hour tube.
 4. The improvement as claimed in claim 1, in which the hour tube is beared on the outside of the bearing element and the minute tube on the inside of said bearing element.
 5. The improvement as claimed in claim 1, in which the hour tube is part of an hour wheel which drives a calendar device.
 6. The improvement as claimed in claim 1, in which the bearing element is made of ruby, beryllium, glucydur, steel, new silver, or brass. 